Generally, a fan is a very important heat-dissipating mechanism for an electronic device. Since the operating performance, stability and service life of the electronic components of the electronic device are directly influenced by temperature, hence the structure of the fan is designed according to the type and the structure of the electronic device.
The installation of the fan in the electronic device is designed for dissipating heat. For preventing from adversely affecting the electronic device, cooling air is inhaled into the casing of the electronic device through an inlet and heated air is exhausted to the surroundings through an outlet. However, experienced from the operation of the fan, a problem that dust is readily accumulated on the fan blade. If a great deal of dust is accumulated on the fan blade, the output airflow is reduced, and the heat-dissipating efficacy of the fan is impaired. Under this circumstance, the electronic device with the fan is possibly damaged. In addition, the dust accumulated on the fan blade may increase the loading of the fan motor, increase the consumed electric power and shorten the service life of the fan.
For solving the problem of accumulating dust, a fan with a dust-eliminating function had been disclosed. While the electronic device is turned on, the control system for controlling the fan starts to reversely rotate the fan to remove the accumulated dust on the fan blade. Then, the fan is forwardly rotated to dissipate heat. However, since the fan is operated for a long term, the problem of accumulating dust on the fan blade still occurs. In other words, the control system cannot effectively eliminate dust.
As mentioned above, the control system has to dynamically control the forward/reverse rotation of the fan in order to effectively eliminate dust. Moreover, if the accumulated dust on the fan blade is serious, the control system has to control the reverse rotation of the fan to eliminate dust in time. However, this designing concept faces some problems. For example, because of an external force or some other factors, the erroneous judgment of the control system will erroneously switch the forward rotation of the fan to the reverse rotation or erroneously switch the reverse rotation of the fan to the forward rotation. Under this circumstance, the fan cannot effectively dissipate heat of the electronic device or eliminate dust.
Moreover, the electronic device is equipped with a protection mechanism. The protection mechanism is enabled or disabled according to the result of judging whether the fan is normally operated. In case that the fan is normally operated (e.g., forward rotation or reverse rotation), a main circuit of the electronic device judges that the fan is normal and the protection mechanism is disabled. Whereas, in case that the fan is abnormally operated and/or stopped, the main circuit judges that the fan is abnormal and the protection mechanism is enabled. The protection mechanism can prevent damage of the electronic device because of the overheating problem. In other words, even if the control system can dynamically control the forward/reverse rotation of the fan, the erroneous judgment still possibly occurs. In the transition interval when operation of the motor is switched between the forward rotation and the reverse rotation, the fan is gradually stopped because of inertia (i.e., in an inertia stop state time period). In the inertia stop state, the main circuit erroneously judges that the fan is abnormal, and thus the protection mechanism is enabled. Under this circumstance, the performance of the electronic device is impaired. Therefore, how to design a control system capable of dynamically controlling operation of the fan to be switched from forward rotation to reverse rotation in real time and avoiding enabling a protection mechanism erroneously without modifying a greater portion of the inner circuitry of the control system and employing additional circuitry and control method are major research and development topics.
Therefore, there is a need of providing a control system and a control method for controlling a forward/reverse rotation of a fan so as to overcome the above drawbacks.